The MR-9 Battery Adapter

MR-9 Battery adapter

I have previously written about adapting a 675 hearing aid battery for use in cameras that require a 1.35 volt PX625. I was pretty confident at the time that since hearing aid batteries operate at 1.4v that this was the solution to this problem… I have since found out that actually, this solution is not always quite as ideal as I had originally thought.

I recently bought a Leica M3; with it came a Leica MR-4 meter. The Leica MR-4 requires a 1.35v px625 shaped battery. No problem I thought, I will just do my usual trick of padding the battery compartment with playdoh or blutak. Unfortunately, this doesn’t work with the MR-4; it didn’t matter how tight I packed the battery compartment, the connection wasn’t quite positive enough and the meter would stop working in the field. When this happened, I would have to take it off the camera, open the bottom, prod at the blutak a bit… … etc. The photo would be missed.

The solution was initially to try a modern 1.55v PX625. Whilst the battery fit tightly, the voltage was so wrong I would have to adjust the ISO setting to compensate. Normally, this doesn’t bother me, but with a Leica, I just wanted it to be right!

Leica MR-4 with px625

Battery check on the Leica MR-4 – The needle is supposed to be over the white dot – With the PX625 it is quite far out.

A quick search on google and I find the MR-9 battery adapter on Small Battery Company’s website. A website that, by coincidence, had been recommended to me just the day before!

I’ll let you read the technical specs and limitations of this adapter on the Small Battery Company’s website, as they are the experts here. But in short, it allows the use of the very common 386 battery in cameras that require a 1.35v mercury oxide MR9, PX13 or PX625 battery. It does this not only by adapting the shape of the battery, but also by lowering the 1.5v of the 386 to 1.35v.

In the following 3 photos you can see the MR-9 battery adapter on the left, with a modern PX625 on the right.


MR-9 with 386 battery vs px625

Positive side faced up

MR-9 with 386 battery vs px625

Negative side faced up with the MR-9 battery adapter empty

MR-9 with 386 battery vs px625

Negative side faced up with the MR-9 battery adapter with 386 battery slotted in


Here you can see the MR-9 battery adapter fitting perfectly inside the Leica MR-4

Leica MR-4 with MR-9 Adapter in bottom

And finally, the moment of truth… The MR-9 battery adapter giving the Leica MR-4 the correct voltage.

Leica MR-4 with MR-9 Adapter

Works perfectly! The only disadvantage of this solution is the price… At nearly £30 the MR-9 battery adapter is not cheap. Though I suspect this price is due to the economies of small quantity manufacture. And actually, since it is only an adapter, after the initial purchase, it will never run out of power itself, it will just need topping up with the abundant and fairly inexpensive 386 batteries.

Lastly, just a quick thanks to the Small Battery Company who shipped the adapter to me very promptly! I know who I will be buying my camera batteries from in the future!

Cheers for reading!


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  • Reply
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  • Avatar
    April 21, 2019 at 7:14 pm

    If you apply a volt meter to a 386, properly inserted into a MR-9 adapter, should it read 1.35 volts on the volt meter. Reason I ask, is that I have a 386 that reads 1.58 on my voltmeter – outside the MR-9 and 1.53 in the adapter I was expecting something closer to 1.35 in the adapter

    • Avatar
      Hamish Gill
      April 21, 2019 at 8:11 pm

      Is it a proper one or a cheap one off ebay – the proper ones contain a resister I think

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